Traditionally, vaccines have been based on live attenuated, or inactivated microorganisms. However, in many instances these strategies are inefficient due to factors such as antigenic variability of microorganisms such as bacteria or fungi. Peptide vaccines that consist of antigenic peptides or peptide fragments of microorganisms have been developed. Conserved peptide fragments are less likely to exhibit antigenic variability, and can overcome some of the problems associated with traditional peptides. Accordingly, subunit vaccines have been developed that target conserved regions of microorganisms. However, synthetic peptide vaccines tend to be poorly immunogenic, and also tend to induce humoral antibody responses, but are less able to induce cell-mediated responses.
With the emergence of drug resistant and/or virulent strains of microorganisms, there is a need for a more effective vaccine against a wide variety of infectious microorganisms.